The present invention relates to methods for creating an object made by means of stereo lithography or another rapid prototype production method and, more particularly, is directed to an improved method for generating a support for an object made by means of stereo lithography or another rapid prototype production method. The present invention also relates to the support created by any of the above methods and to software adapted to carry out any of the above methods. The present invention also relates to a controller for controlling a rapid prototype production machine.
Rapid Prototyping and Manufacturing (RP&M) can be defined as a group of techniques used to quickly fabricate a scale model of an object typically using three-dimensional (3-D) computer aided design (CAD) data of the object. Currently, a multitude of Rapid Prototyping techniques is available, including stereo lithography (SLA), Selective Laser Sintering (SLS), Fused Deposition Modeling (FDM), foil-based techniques, etc.
A common feature of these techniques is that objects are typically built layer by layer. Stereo lithography, presently the most common RP&M technique, utilizes a vat of liquid photopolymer “resin” to build an object a layer at a time. On each layer, an electromagnetic ray, e.g. one or several laser beams which are computer-controlled, traces a specific pattern on the surface of the liquid resin that is defined by the two-dimensional cross-sections of the object to be formed. Exposure to the electromagnetic ray cures, or, solidifies the pattern traced on the resin and adheres it to the layer below. After a coat had been polymerized, the platform descends by a single layer thickness and a subsequent layer pattern is traced, adhering to the previous layer. A complete 3-D object is formed by this process.
Selective laser sintering (SLS) uses a high power laser or another focused heat source to sinter or weld small particles of plastic, metal, or ceramic powders into a mass representing the 3-dimensional object to be formed.
Fused deposition modeling (FDM) and related techniques make use of a temporary transition from a solid material to a liquid state, usually due to heating. The material is driven through an extrusion nozzle in a controlled way and deposited in the required place as described among others in U.S. Pat. No. 5,141,680.
Foil-based techniques fix coats to one another by means of gluing or photo polymerization or other techniques and cut the object from these coats or polymerize the object. Such a technique is described in U.S. Pat. No. 5,192,539.
For most RP&M techniques, it is necessary to anchor the object (i.e. the part) to a platform by means of a support to keep the object in place during the production process. These supports also prevent the object against deformations as it is being constructed. For example, stereo lithography resins have a tendency to deform during the building process because of internal stresses generated by shrinkage resulting in curling effects.
Once the production of the part is completed, it is necessary to manually separate the part from the temporal support. Preferably, this separation step requires a minimal effort and does not damage the surface or fine features of the object. To allow an easy removal of the support, it is already known that providing the walls with notches at the top and/or the bottom restrict the contact with the object and make it easier to remove the support.
Moreover as the support is removed once the object is built, the support is considered as lost material. It is therefore preferred to minimize the time, energy and amount of material required to build the support. Techniques to lower the material cost of the support are, for example, described in U.S. Pat. No. 5,595,703. On the other hand, the supports needs to maintain a sufficiently large structural strength to accommodate for the forces acting during part construction, e.g., gravitational, tensile, etc.
Typically RP&M techniques start from a digital representation of the 3-D object to be formed. Generally, the digital is sliced into a series of cross-sectional layers which can be overlaid to form the object as a whole. The RP&M apparatus uses this data for building the object on a layer-by-layer basis. The cross-sectional data representing the layer data of the 3-D object may be generated using a computer system and computer aided design and manufacturing (CAD/CAM) software. In this case, the support can be created by the CAD system as well. However, as this tends to be a tedious and labor intensive task, software has been developed in the past to automatically design the support structures and transcribe them in STL or any other surface format which gives a description of the special structure. Prior to designing the support, it is preferred to convert the 3-D CAD model into layers. One of the advantages to this approach is that a technique well known to those skilled in the art as beam width compensation may be applied to the generated slices. As this technique converts the layers into a geometry that corresponds more to the layers built by the production system, it typically results in a more accurate support. A software tool named the Contour Support generator (CSUP), as developed by Materialise N.V., Leuven, Belgium, is a first example of a tool that automatically designs a support structures based on the layer data of the object to be formed. Another method for automatic support generation is disclosed in patent application U.S. Pat. No. 5,943,235.
One of the disadvantages of the above-mentioned software tools is that often, the designed support does not sufficiently support at least one region of the object. Consequently, it is often required to verify the generated support and add extra support manually where needed. As mentioned earlier, this is a tedious and labor intensive task. Accordingly, those skilled in the art of rapid prototyping and the like have long recognized the desirability for further improvement in a more rapid, reliable and automatic means which would facilitate the design of supports to overcome the disadvantages of the prior art.